Chemical Geology最新文献

{"title":"Melt‑carbonate metasomatism in the Sulu orogen: Implications for CO2 release in the continental subduction zone","authors":"Shaoji Yang ,&nbsp;Pan Wang ,&nbsp;Haijin Xu ,&nbsp;Fan Feng","doi":"10.1016/j.chemgeo.2025.123217","DOIUrl":"10.1016/j.chemgeo.2025.123217","url":null,"abstract":"<div><div>Subduction zone carbon cycling governs the carbon budget balance between Earth's interior and surficial systems and constrains long-term climatic-environmental evolution. While extensive research has focused on oceanic subduction zones, CO₂ release mechanisms in continental subduction zones remain poorly understood. The Sulu orogen, which experienced cold subduction followed by hot exhumation and extensive anatexis, provides an ideal natural laboratory for investigating carbon release processes in continental subduction zones. Petrology, mineral chemistry, and titanite geochronology were conducted to investigate a melt-metacarbonate interaction profile, where the migmatite – contact zone (calc-silicate rock) - marble system clearly records CO₂ release and migration. Petrographic and mineral chemical analysis reveal diverse metasomatic reactions between silicate melts and marble. In the innermost marble, limited melt infiltration led to olivine and phlogopite formation with CO₂ release. At the contact zone, intense metasomatic reactions produced diopside, tremolite, scapolite, and titanite, releasing substantial CO₂. The metasomatism also induced carbon migration through calcite-bearing melt/fluid, including calcite-bearing silicate melts near the migmatite, quartz + calcite ± tremolite veins and calcite veins in the contact zone, and carbon-bearing serpentine veins in the marble. Titanite U-Pb age (206 ± 0.7 Ma) and Zr-in-titanite thermometer (<em>T</em> = 792–862 °C) suggest the CO₂ release occurred at the exhumation stage. These findings demonstrate that metamorphic decarbonation occurs not only in hot subduction zones but also during hot exhumation of cold subducted slabs, providing new insights into carbon cycling in continental subduction zones and helping address carbon budget imbalance in global carbon cycling models.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123217"},"PeriodicalIF":3.6,"publicationDate":"2025-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145796051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Photochemistry of Fe (II) and carbonate-bearing waters and the influence on Greenhouse Gas production in Early Mars","authors":"V.B. Rivera Banuchi ,&nbsp;J. Gong ,&nbsp;E.N. Mansbach ,&nbsp;T. Bosak ,&nbsp;J.A. Hurowitz","doi":"10.1016/j.chemgeo.2025.123210","DOIUrl":"10.1016/j.chemgeo.2025.123210","url":null,"abstract":"<div><div>Aqueous iron UV photooxidation, a proposed pathway for early Martian iron deposits produced in surface environments, produces hydrogen gas, a potentially important greenhouse gas for early Mars. This experimental study focused on iron photooxidation in the presence of dissolved inorganic carbon (DIC) at a range of concentrations that represent partial pressures of CO₂ (0.1–1 bar), consistent with estimated atmospheric pressures and compositions on early Mars. We report in-situ sampling of gas headspace to understand the extent to which DIC impacts the production of hydrogen gas that may be produced from aqueous iron photooxidation. The experiments demonstrate that ferrous iron photooxidation does not occur at any of the tested DIC concentrations (3.4–35 mM). Ferrous iron carbonate minerals were precipitated at pH conditions above 6, while maintaining relatively high dissolved iron concentrations at siderite saturation. We observed hydrogen and methane gas production at varying initial conditions, but no clear relationships to either iron loss to oxidation and/or precipitation or DIC concentrations could be inferred. Instead, we suggest that hydrogen is a byproduct of methane photolysis. The methane itself was sourced from an unknown background organic carbon compound from residual organic impurities in the deionized water source utilized in the experiments and is unrelated to iron photochemistry. These observations indicate that iron photooxidation is an unlikely mechanism to have produced hydrogen and precipitated iron oxide minerals at near-neutral pH in the presence of 0.1–1 bar CO₂ on early Mars.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"703 ","pages":"Article 123210"},"PeriodicalIF":3.6,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786145","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A multi-isotope deconvolution approach to correct for hydride and xenon interferences during double spike barium isotope analyses with MC-ICP-MS","authors":"Qasid Ahmad ,&nbsp;Hongjie Zhang ,&nbsp;Sune G. Nielsen","doi":"10.1016/j.chemgeo.2025.123209","DOIUrl":"10.1016/j.chemgeo.2025.123209","url":null,"abstract":"<div><div>Precise and accurate stable barium isotope (δ^138/134Ba relative to the NIST3104a standard) measurements are crucial for geochemical studies, as natural variations can be small. Double spike Ba isotope analysis by MC-ICP-MS is typically the preferred method for generating reliable Ba isotope data as it effectively corrects for instrumental mass fractionation and isotope fractionation during chemical separation, while also providing precise concentrations via isotope dilution. However, measurement of 50 ng or less of Ba using high sensitivity interface cones can be challenging due to the effects of isobaric interferences from trace Xe in the Ar plasma. Here we demonstrate that interferences from Ba-hydrides (BaH⁺) also have significant effects on double spike corrected δ^138/134Ba-values and, therefore, must be assessed and corrected.</div><div>We present a multi-isotope deconvolution strategy utilizing a ¹³⁵Ba–¹³⁶Ba double spike and three independent inversions using different un-spiked isotope pairs (¹³⁴Ba–¹³⁷Ba, ¹³⁴Ba–¹³⁸Ba, and ¹³⁷Ba–¹³⁸Ba) to solve the double spike equation. Each inversion independently calculates δ^138/134Ba that is differently affected by both background Xe and hydride interferences during the measurement. We show that the Xe correction is smallest for the ¹³⁷Ba–¹³⁸Ba inversion, which allows accurate Ba isotope data to be obtained for this inversion even when &lt;5 ng of Ba is consumed during triplicate sample measurements. However, the ¹³⁷Ba–¹³⁸Ba inversion also carries the largest effect from hydride formation, which we correct for using a combined ¹³⁴Ba–¹³⁸Ba/¹³⁷Ba–¹³⁸Ba inversion method. This approach produces long-term external reproducibility for rock reference materials of ±0.025 ‰ (2SD) when consuming less than 50 ng of Ba, which represents an improvement over previously reported Ba double-spike MC-ICP-MS methods at similar Ba consumption. We conclude that the double spike multi-isotope deconvolution approach can accurately assess and correct for elemental and hydride interferences for isotope systems with 5 or more stable isotopes suggesting that isotope systems such as Zr, Mo, Cd, Sn and Te might benefit from this strategy.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"703 ","pages":"Article 123209"},"PeriodicalIF":3.6,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"δ88/86Sr and 87Sr/86Sr variability in fish otoliths: Implications for seawater temperature, growth-rate, and provenance","authors":"Arka Chakraborty ,&nbsp;Sourav Ganguly ,&nbsp;Arild Folkvord ,&nbsp;Steven E. Campana ,&nbsp;Prosenjit Ghosh ,&nbsp;Ramananda Chakrabarti","doi":"10.1016/j.chemgeo.2025.123208","DOIUrl":"10.1016/j.chemgeo.2025.123208","url":null,"abstract":"<div><div>We report stable (δ^88/86Sr) and radiogenic (⁸⁷Sr/⁸⁶Sr) Sr isotopic compositions of natural and laboratory-cultured aragonitic fish otoliths. The natural samples are from five different species collected from the Atlantic Ocean that grew over temperature ranges of 2–25 °C while the cultured samples grew in water temperatures of 4–16 °C. The otoliths exhibit significant variability in δ^88/86Sr values (−0.095 ‰ to 0.102 ‰) and incorporate the lighter ⁸⁶Sr isotope relative to ambient seawater in both natural and experimental settings. The δ^88/86Sr values in natural otoliths negatively correlate with ambient seawater temperature. They show positive and negative correlations with previously reported Δ₄₇ and δ^44/40Ca values, respectively, measured on the same powdered samples. A multi-proxy approach to determine seawater temperature combining δ^88/86Sr, δ^44/40Ca, and Δ₄₇ values and Sr/Ca ratio is proposed, which has an uncertainty of ±0.75 °C and is better than uncertainties when these proxies are used in isolation. Strong correlations are also observed between Sr elemental partitioning (K_D^Sr/Ca) and Δ^88/86Sr (δ^88/86Sr_otolith - δ^88/86Sr_seawater) values in natural otoliths. Although the lighter isotopes of both Sr and Ca are preferentially incorporated in the otolith carbonates, a negative correlation is observed between δ^88/86Sr and δ^44/40Ca values. Contrasting correlations are also observed between K_D^Sr/Ca and Δ^88/86Sr values as well as K_D^Sr/Ca and Δ^44/40Ca (δ^44/40Ca_otolith - δ^44/40Ca_seawater) values, suggesting different carbonate crystallization pathways for Sr and Ca isotopes.</div><div>The δ^88/86Sr values of cultured otoliths overlap with natural otolith samples but their K_D^Sr/Ca values are lower than the natural samples. While no relationship is observed between δ^88/86Sr values, water temperatures, and K_D^Sr/Ca values, growth rate shows a positive correlation with water temperature in cultured otoliths. The Δ^88/86Sr* values (Δ^88/86Sr normalized to growth rate) of the cultured otoliths show positive and negative correlations with K_D^Sr/Ca* (K_D^Sr/Ca corrected for growth rate) values and temperature, respectively, consistent with observations from natural otoliths. The δ^88/86Sr values do not show any correlation with ⁸⁷Sr/⁸⁶Sr ratios. Variability in ⁸⁷Sr/⁸⁶Sr ratios in the natural otoliths reflect their provenance from coastal oceans, which receive varying amounts of continent-derived freshwater.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123208"},"PeriodicalIF":3.6,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"From bacterial to thermochemical sulfate reduction: Sulfur isotope constraints on the genesis of hyper-enriched black shales","authors":"Kyle M. Henderson ,&nbsp;James R. Clark ,&nbsp;Anthony E. Williams-Jones ,&nbsp;Ryan Sharpe ,&nbsp;Mostafa Fayek","doi":"10.1016/j.chemgeo.2025.123207","DOIUrl":"10.1016/j.chemgeo.2025.123207","url":null,"abstract":"<div><div>Hyper-enriched black shales (HEBS) are thin stratiform and stratabound sulfide-rich (∼70 vol%) units that have percentage level concentrations of metals such as Ni, Mo and Zn. In the Peel River area of Yukon, Canada, HEBS are highly enriched in Ni (∼3 wt%), Zn (∼0.2 wt%), and Mo (0.2 wt%), hosted mainly by millerite (NiS), sphalerite (ZnS) and pyrite (FeS₂). The processes that control millerite-sphalerite precipitation in HEBS are poorly constrained. Here, we report the first in-situ sulfur isotope measurements of sulfide minerals in the Peel River HEBS. Early diagenetic pyrite (δ³⁴S -31.9 ± 9.0 ‰) formed in response to open-system bacterial sulfate reduction (BSR), whereas later sphalerite (16.5 ± 5.1 ‰) and millerite (+10.0 ± 1.4 ‰) crystallized via thermochemical sulfate reduction. We have developed a three-stage model for HEBS formation. Stage 1 involves high primary productivity, a redox-stratified water column, a low sedimentation rate, and an active Fe-oxide shuttle, which promoted BSR-driven pyrite precipitation. Organic matter scavenged Ni and Zn from the water column and pore-water, producing metal-rich kerogen. Stages 2 and 3 occur during late diagenesis, with the infiltration of an acidic, oxidized, metal-poor, sulfate-bearing brine that interacted with the metal-bearing kerogen, triggering thermochemical sulfate reduction and millerite-sphalerite precipitation. Subsequent fracturing and increased fluid-flow during peak hydrocarbon generation caused acid-driven replacement of sphalerite by a second generation of millerite. This model accounts for HEBS formation in both Canada and China, demonstrating that, although late-stage fluids did not transport the metals, brines were essential to their genesis.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123207"},"PeriodicalIF":3.6,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The predominance of SiO5 species in MgSiO3 melt at transition zone pressures from a dynamics point of view","authors":"Georg Spiekermann ,&nbsp;Maximilian Schulze","doi":"10.1016/j.chemgeo.2025.123194","DOIUrl":"10.1016/j.chemgeo.2025.123194","url":null,"abstract":"<div><div>Ab initio molecular dynamics (AIMD) simulations of melt and glass of MgSiO₃ and of other compositions at high pressure consistently observe the predominance of fivefold-coordinated silicon ( <figure><img></figure> ) over <figure><img></figure> and <figure><img></figure> in the pressure range of the mantle transition zone. However, the common approach to compute the abundance of different coordination states is only based on a static ‘sequential-3D’ structural analysis. The absence of a time scale in the analysis has led to concern about the validity of its results. To validate AIMD results, here we investigate the coordination dynamics beyond the static limit, by carrying out a dynamical coordination species analysis in ‘4D’ on the basis of the short-term part of the intermittent coordination autocorrelation function described in an earlier study. We found that the predominance of SiO₅ species at pressures of the transition zone is persistent even in a dynamical analysis. However, towards lower pressures and most pronounced at ambient pressure, the majority of all SiO₅ detected by the common static sequential-3D analysis are so short-lived that they should be considered ‘spurious’ rather than chemical species.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123194"},"PeriodicalIF":3.6,"publicationDate":"2025-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785274","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Epidote emerges as a pivotal player in the hydration dynamics of the mantle transition zone","authors":"Jing Gao ,&nbsp;Xueyin Yuan ,&nbsp;Xinyang Li ,&nbsp;Chaowen Xu ,&nbsp;Yue Wang ,&nbsp;Wanghua Wu","doi":"10.1016/j.chemgeo.2025.123206","DOIUrl":"10.1016/j.chemgeo.2025.123206","url":null,"abstract":"<div><div>Geophysical data has revealed anomalous water enrichment in the mantle transition zone (MTZ, 410–660 km depths), which is widely attributed to crustal water released from stagnant subducted slabs. However, the majority of hydrous minerals dehydrate completely at depths &lt;∼300 km, leaving the mechanism of water transport to the deeper mantle unresolved. The discovery of ‘epidote-phases’ in superdeep diamonds from the MTZ offers a potential solution, yet critical uncertainties persist regarding its stability under subduction-zone thermal gradients and MTZ conditions. This study experimentally demonstrates that the hydroxyl groups in epidote strengthen along cold-to-hot subduction geotherms (5–25 °C/km) across ∼250 km. In the deeper reduced mantle (buffered by FeO-Fe), epidote undergoes complete dehydration at ∼250 km via decomposition into grossular, andradite and wustite. Yet, kinetic barriers and the limited extent of reduced domains within slabs probably inhibit this process. Under oxidized conditions (Fe₂O₃-Fe₃O₄ buffer), epidote destabilizes at thermally perturbed slab interfaces, and is more likely to decompose via prolonged mantle-derived heating in the MTZ. This breakdown partially traps water in the newly formed grossular garnet. These findings redefine epidote as a dynamic agent in the hydration of the MTZ, offering a novel mineralogical perspective on the water-rich characteristics of this enigmatic region.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123206"},"PeriodicalIF":3.6,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145766047","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mineralization of bacterial cells during proto-dolomite precipitation mediated by the halophilic bacteria Bacillus licheniformis","authors":"Ruirui Meng ,&nbsp;Zuozhen Han ,&nbsp;Wen Nie ,&nbsp;Chao Han ,&nbsp;Yu Han ,&nbsp;Maurice E. Tucker","doi":"10.1016/j.chemgeo.2025.123205","DOIUrl":"10.1016/j.chemgeo.2025.123205","url":null,"abstract":"<div><div>Previous studies have demonstrated that bacteria can induce proto-dolomite precipitation at ambient temperatures. Yet, the mineralization of the bacteria during this process has rarely been reported. Here we describe mineralized bacteria formed during proto-dolomite precipitation mediated by the moderate halophilic bacteria <em>Bacillus licheniformis</em> Y1. The XRD data and SEM images show that proto-dolomite precipitated mainly as aggregates in media with Mg/Ca ratios of 6, 8 and 10 cultured at temperatures of 30 °C and 40 °C, but this was not observed in solutions cultured at 20 °C. Solution chemistry analysis showed that all solutions maintained a higher CO₃²⁻ concentration and correspondingly higher saturation indices for proto-dolomite at 40 °C. The HRTEM results illustrate that the crystal structures and Mg/Ca atomic ratio of the proto-dolomite more closely match those of dolomite, and some superstructure reflections appear in the HRTEM and SAED images. These features indicate that a few crystal units of proto-dolomite may have been formed with some degree of cation ordering. The SED/EDS and HRTEM images also demonstrate that the bacteria are mineralized and form proto-dolomite crusts. The HTREM analyses of bacterial ultrathin slices show that the proto-dolomite crystals formed within cells, on the cell surface and within EPS. We assume that during biomineralization, Ca²⁺ and Mg²⁺ ions are trapped by the negatively charged EPS and transferred into the cells through diffusion, leading to the extracellular and intracellular precipitation of proto-dolomite; the bacteria themselves are mineralized during the constant formation of proto-dolomite crystals within and upon the surface of the cells. This study provides insights into our understanding of the formation of biotic proto-dolomite, and contributes to the origin of “microbial dolomite”.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"701 ","pages":"Article 123205"},"PeriodicalIF":3.6,"publicationDate":"2025-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145753515","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Proterozoic highly siderophile element enrichment of the Kaapvaal cratonic Archean mantle","authors":"Nadine P. Cooper ,&nbsp;D. Graham Pearson ,&nbsp;Andreas Auer ,&nbsp;Tristan Bongartz ,&nbsp;Yannick Bussweiler ,&nbsp;Mario Fischer-Gödde ,&nbsp;Max Hellers ,&nbsp;Geoffrey Howarth ,&nbsp;Andrew J. Locock ,&nbsp;Ambre Luguet ,&nbsp;Carsten Münker ,&nbsp;Thomas Stachel ,&nbsp;Ashlea N. Wainwright ,&nbsp;Sarah Woodland ,&nbsp;James M. Scott","doi":"10.1016/j.chemgeo.2025.123201","DOIUrl":"10.1016/j.chemgeo.2025.123201","url":null,"abstract":"<div><div>The c. 86 Ma Jagersfontein kimberlite in the southern portion of the Kalahari craton in South Africa erupted a suite of refractory peridotite xenoliths with regionally anomalous rhenium+osmium (Re<img>Os) isotope systematics and highly siderophile element (HSE) abundances. A portion of this suite comprises peridotites with 2.7 to 3.0 Ga Re- depletion ¹⁸⁷Os/¹⁸⁸Os model ages, refractory major elements and HSE abundances that represent some of the most depleted and least metasomatised known components of Archean cratonic nuclei. Other peridotites in the Jagersfontein suite show enrichment in Os, Ir, Pd, Pt and, especially, Ru, as well as having more radiogenic ¹⁸⁷Os/¹⁸⁸Os. Ruthenium abundances reach up to ∼22 times “Primitive Upper Mantle” levels and correspond to samples containing microscopic laurite plus pentlandite. The more radiogenic ¹⁸⁷Os/¹⁸⁸Os in HSE-enriched samples, along with the modern mantle like Ru isotope composition (ε¹⁰⁰0.00 ± 0.12, ε¹⁰²–0.03 ± 0.16), indicate that the prominent HSE enrichment is not related to an excess of unequilibrated Late Veneer material in the mantle source. Instead, the HSE characteristics and Os isotope ratios of these peridotites are inferred to have been caused by metasomatic addition of small volumes of HSE-rich sulfide/alloy to the refractory Archean peridotites. Although there is some variation in the metasomatic characteristics, the calculated ¹⁸⁷Os/¹⁸⁸Os of the contaminant causing the strongly Ru-enriched peridotites is ∼0.116, which is equivalent to the convecting mantle composition in the early Mesoproterozoic. Unlike the erosion and Proterozoic replacement of older mantle interpreted to explain post-Archean ¹⁸⁷Os/¹⁸⁸Os mantle beneath the central Kaapvaal nucleus, the Archean mantle lithosphere beneath Jagersfontein therefore appears to have been modified by the passage of Proterozoic melts. The 2400 km² 1.9 Ga layered mafic Trompsburg Complex, less than 10 km southeast of Jagersfontein, indicates that the mantle lithosphere in the area has experienced substantive transfer of large volumes of post-Archean melt, and we suggest that the passage of those melts may have caused the mantle HSE enrichment.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"702 ","pages":"Article 123201"},"PeriodicalIF":3.6,"publicationDate":"2025-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145731849","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deciphering chemical complexity in monogenetic eruptions: Xitle Volcano, Mexico","authors":"J. Ahmadi ,&nbsp;E. Widom ,&nbsp;M.-N. Guilbaud ,&nbsp;C. Siebe ,&nbsp;D.C. Kuentz ,&nbsp;R. Sanchez ,&nbsp;M. Medina-Jaen ,&nbsp;J.J. Zamorano-Orozco ,&nbsp;S.M. Straub","doi":"10.1016/j.chemgeo.2025.123204","DOIUrl":"10.1016/j.chemgeo.2025.123204","url":null,"abstract":"<div><div>Xitle Volcano, an ∼1700-year-old scoria cone located at the southern edge of Mexico City and within the central Trans-Mexican Volcanic Belt (TMVB), provides a unique opportunity to investigate the causes of geochemical diversity in monogenetic eruptions. We present the first integrated major-trace element and Sr–Nd–Pb–Os isotopic dataset which, coupled with new stratigraphic mapping and petrologic observations of Xitle's eruptive products, provides constraints on the roles of mantle heterogeneity, subduction-related metasomatism, and crustal assimilation in Xitle magma genesis. The lavas and tephras range in composition from basalt to basaltic andesite and basaltic andesite/basaltic trachyandesite. All samples have arc-like trace element patterns with enrichments in large ion lithophile elements and depletions in high field strength elements, with early-stage magmas exhibiting stronger arc-like signatures, while later magmas trend toward intraplate affinities. Isotopic compositions span ⁸⁷Sr/⁸⁶Sr = 0.70335–0.70398, ¹⁴³Nd/¹⁴⁴Nd = 0.512790–0.512953, ²⁰⁶Pb/²⁰⁴Pb = 18.667–18.770, ²⁰⁷Pb/²⁰⁴Pb 15.570–15.612, and ²⁰⁸Pb/²⁰⁴Pb = 38.355–38.554. ¹⁸⁷Os/¹⁸⁸Os ratios range from 0.1368 to 0.1968, with Os concentrations between 10.7 and 168.4 pg/g. These ¹⁸⁷Os/¹⁸⁸Os values are more radiogenic than the primitive upper mantle (∼0.1296) and fall within the range observed for other arc magmas in the TMVB. The samples collectively define three distinct compositional groups, but the compositional variations do not evolve monotonically with time; rather abrupt compositional and isotopic shifts occur over the course of the eruption. Neither closed system fractional crystallization nor assimilation-fractional crystallization of a single parental magma can reproduce the observed geochemical range. Instead, we propose an open-system scenario involving high-temperature fractional crystallization periodically interrupted by recharge events from compositionally and isotopically distinct magmas, supported by MELTS and Magma Chamber Simulator (MCS) modeling. Isotope systematics argue against significant crustal assimilation and point to a heterogeneous, subduction-metasomatized mantle wedge as the primary source of the magmas from Xitle. The mantle source beneath Xitle was variably fluxed by two distinct slab-derived components, both dominated by terrigenous sediment with variable inputs of altered oceanic crust (AOC)-derived fluid/melts, in relative proportions that evolved over time. Our results demonstrate that Xitle's chemical complexity reflects serial addition of subduction fluids, partial melting of a compositionally evolving mantle source, and repeated magma recharge, emphasizing that even small monogenetic systems can record prolonged and multi-stage magmatic histories of mantle derived melts.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"703 ","pages":"Article 123204"},"PeriodicalIF":3.6,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145731851","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}